This patient has a narrow-complex tachycardia with a regular rhythm. A narrow QRS complex is defined as a QRS interval less than 120msec. This is a normal finding. The differential diagnoses for regular narrow complex tachycardia include sinus tachycardia, atrial tachycardia, atrial flutter, and supraventricular tachycardia (“SVT”). SVTs are typically associated with narrow QRS complexes, unless there is a concurrent bundle branch block, other aberrant conduction, or the existence of electrical accessory pathways as in Wolff Parkinson White (WPW) syndrome. The heart rate of an SVT can vary from 140-280 beats/min. Intravenous Adenosine (Choice A) is a hallmark of SVT treatment, however, Adenosine is given after vagal maneuvers have been attempted and have failed. Synchronized cardioversion (Choice B) is a last-ditch effort treatment in a patient with SVT. Vagal maneuvers and medications are attempted prior to using cardioversion. However, if the patient is hypotensive, cardioversion should be employed. Intravenous Amiodarone (Choice C), beta-blockers, calcium channel blockers, or other antiarrhythmics can be used to terminate SVTs if vagal maneuvers and adenosine are not effective. Vagal maneuvers (Choice D), such as the Valsalva maneuver (“bearing down”) or carotid massage, are the initial treatment for SVTs. Correct Answer: D